The present invention is directed to a device for humidifying the intake air of an internal combustion engine, which is equipped with a turbocharger.
It is known to humidify the intake air of Diesel engines, which are equipped with turbochargers, in order to reduce the NOx portion in the exhaust gas in this manner. Such a method with associated device is described in WO 95/23 286. According to this publication a humidifying means is used which is passed by the intake air and water, wherein the intake air, prior to the humidification, is compressed by the compressor of the turbocharger and the energy residing in the cooling water or the exhaust gases of the internal combustion engine is used for pre-heating the water before the same is introduced into the humidifying means. Accordingly, compressed air is humidified.
From EP 1 076 169 A2 a device for humidifying the intake air of internal combustion engines, which are equipped with a turbocharger, is known which comprises a humidifying means through which the intake air and humidifying liquid flow and contact with one another and which is located upstream from the compressor of the turbocharger in flow direction of the intake air, and an air/air heat exchanger located upstream from the humidifying means in the flow path of the intake air and serving for pre-heating the intake air, said air/air heat exchanger being passed by the atmospheric intake air and the humidified and compressed intake air from the compressor. Accordingly, due to this solution the intake air is humidified in a non-compressed condition. The pre-heating of the intake air is realized by means of an air/air heat exchanger which is passed by the compressed intake air.
It is the object of the invention to provide a device of the indicated kind with which the intake air can be pre-heated in an especially effective and practical manner for humidification.
According to the invention this object is obtained with a device of the cited kind by the feature that the device includes a heat exchanger, serving for pre-heating the intake air, which is flown through by the atmosperic intake air and which is located in a liquid circuit (water circuit) with which the humidified intake air compressed by the compressor, which is fed to the internal combustion engine, is cooled by means of a further heat exchanger.
Accordingly, due to the invention no air/air heat exchanger as with the above-cited prior art is used but instead an air/liquid heat exchanger which is located in a liquid circuit (water circuit) which includes a further heat exchanger. This further heat exchanger is also an air/liquid heat exchanger which is flown through by the compressed and humidified intake air coming from the compressor. In this further heat exchanger the compressed and humidified intake air for the internal combustion engine is cooled, i.e. it delivers a part of its heat energy to the liquid circuit with which this heat energy is transferred to the intake air in the heat exchanger serving for pre-heating the intake air which is pre-heated in this manner for the following humidification.
The liquid circuit is preferably a water circuit.
The inventive solution has a number of advantages. Firstly, means which are already present can be used for carrying out the pre-heating of the intake air for humidification in many cases, especially with internal combustion engines which already have a charging air cooler. In these cases the charging air cooler which is already present can be redesigned in order to serve as further heat exchanger in the liquid circuit for the invention. Even if such a charging air cooler is not used, instead of the same the further heat exchanger can be disposed so that the space necessary for the inventive solution is reduced. Secondly, further means, as for instance exhaust gas heat exchangers, oil heat exchangers (oil coolers), can be incorporated into the liquid circuit if the operation conditions of the internal combustion engine make this desirable.
Accordingly, the further heat exchanger in the liquid circuit is a charging air cooler (intercooler), especially a charging air cooler which is already present and which is redesigned correspondingly. So, preferably the existing charging air cooler of the internal combustion engine of a ship is used as further heat exchanger wherein the sea water circuit of the charging air cooler is used as liquid circuit into which the heat exchanger is incorporated (with correspondingly modified sea water circuit).
According to the invention the compressed and humidified intake air coming from the compressor is cooled in the further heat exchanger (charging air cooler). Such a cooling is desired wherein, however, a condensation of the compressed and humidified air has to be avoided. According to the invention this is preferably achieved in such a manner that the liquid circuit includes a bypass valve and a bypass line which enable recirculating of the liquid coming from the heat exchanger to the heat exchanger without flowing through the further heat exchanger. If, for instance, a sensor determines that further cooling of the compressed and humidified intake air would result in a condensation, the bypasse valve will be opened and the liquid coming from the heat exchanger will be partly recirculated to the heat exchanger without passing the further heat exchanger. Accordingly, the liquid circuit is partly short-circuited which has the result that the humidified and compressed intake air is less cooled in the further heat exchanger (charging air cooler). By closing the bypass valve the liquid circuit can be again operated in its normal operation cycle. Accordingly, the cooling of the humidified and compressed intake air can be regulated with the bypass valve.
The inventive solution is characterized by an especially simple design since it is relatively uncomplicated to install two different but on principle identical heat exchangers in a spaced condition and to connect the same by means of a liquid circuit (water circuit). For this, only a liquid tube system with a pump is necessary.
Preferably, a droplet separator is located behind the further heat exchanger.
The remaining components of the device for humidifying the intake air of the internal combustion engine can be substantially designed in such a manner as described in the above-cited EP 1 076 169 A2. So, especially upstream from the mentioned heat exchanger located in the liquid circuit further humidifying stages with upstreamly disposed air heating means can be provided. The air heating means can be heat exchangers which are, for instance, flown through by the cooling water of the internal combustion engine. Details of these further components are no more mentioned here. It is rather pointed to the disclosure of EP 1 076 169 A2.